to answer the original question RMS is the power rating that the speakers/amp can play consistenly PMPO is basically thye point at which the speakers/amp will blow up. I've been in testing labs for an international company while they were doing these tests, and they did literally blow the speaker up to test PMPO.
At the end of the day though guys, it really doesnt matter what your speakers are rated at, as you are FAR more likely to blow a speaker up by under powering it. How? Simply by overworking your amplifier so sending a 'clipped' signal to the speakers. A clipped signal is what causes distortion and this is the MAIN cause of damaged speakers. For those of you that dont know what a 'clipped' signal is I'll explain. Normally an amplifier outputs a sinewave, a sine wave looks like this -
\/\/\/\/\/\/\/\ but smooth and curvy
a clipped signal is when the amplifier cannot make this wave larger and so cuts the peaks and troughs off of the sine wave, hence its called clipping, this makes the nice smooth sine wave look like this -
\_/-\_/-\_/-\_/
Basically, what I am saying is, dont worry about what the power HANDLING of a speaker is, as you are VERY unlikely to blow it up from over powering it. You want a good headunit that provides a clean signal to the amp, a good amp to amplify the signal without clipping and then speakers. You can improve the sound by putting better speakers in, but they will only ever be as good as what comes before it, so basically the head unit should ALWAYS be the best part of the system, then the amp then the speakers. I have run systems - admitedly in home hifi setups - that are fronted by £2000 cd players, then a £2000 pre/power amplifier combination running £200 speakers, and the sound from that was better than any other system I could put together for around £4000!